Modern data center deployments typically span multiple sites, each with its own local network. The multiple sites are generally interconnected via a larger network, referred to herein as a core network. Each site includes one or more network devices, referred to herein as edge devices (nodes), that facilitate the transport of information between the local network and the core network (i.e., originate or terminate communications over the core network). The sites also include one or more intermediate network devices (nodes) that facilitate the operation of the local network for the communications between computing devices in the site and the edge devices.
A virtual private network (VPN) is a private network that uses a public network (e.g., core network) to connect the remote sites. The VPN uses “virtual” connections routed through the core network so that the devices at the different sites can securely share information and resources. In certain circumstances, a VPN may be established through the use of an Overlay Transport Virtualization (OTV) mechanism. The OTV mechanism provides an “overlay” method of virtualization (rather than traditional “in-the-network” methods in which multiple routing and forwarding tables are maintained in every device between a source and a destination). A VPN established using the OTV mechanism is sometimes referred to herein as an overlay network.